Output current control method and device of virtual synchronous machine

Abstract

The present application discloses a method and device for controlling the output current of a virtual synchronous machine in response to unbalanced grid voltage. The method includes: extracting the negative sequence voltage component in the grid connection point voltage of the virtual synchronous machine, and performing phase compensation on the negative sequence voltage component to obtain a negative sequence voltage action 1; superimposing the negative sequence voltage action 1 with the basic voltage action in the target coordinate system to obtain a final voltage action; modulating the final voltage action to generate a driving signal required for the control of the virtual synchronous machine. The present application extracts the negative sequence component of the grid connection point voltage of the virtual synchronous machine and performs phase compensation, and then superimposes it on the basic voltage action, without increasing the system cost, so that the output current can be kept balanced when the grid voltage is unbalanced, and the overcurrent risk when the grid voltage drops can be reduced, thereby improving the operation capability of the virtual synchronous machine to adapt to the unbalanced grid voltage.

Description

Technical Field

[0001] The present application relates to the field of power electronics technology, and in particular to an output current control method and device for a virtual synchronous machine to cope with grid voltage imbalance. Background Art

[0002] Most traditional renewable energy grid-connected units operate in a controlled current source CSC mode that follows the grid operation and do not actively participate in the grid frequency regulation. Existing research results show that the CSC operation mode will lead to a decrease in grid inertia, which poses a severe challenge to the safe operation of the power system in the context of high penetration of renewable energy grid connection.

[0003] Only when the power grid is safe and stable can clean energy improve its own survival ability. In the scenario of large-scale access to new energy power generation, the previous control idea of ​​"only focusing on power generation, not the power grid" will become increasingly difficult to meet the requirements of stable operation of the power system. Having a certain grid voltage amplitude and frequency support capability, relying on flexible and controllable power electronics technology, enhancing the ability to serve the power grid, and jointly contributing to the maintenance of the current power grid security and stability are also the requirements of the new grid-connected guidelines for future new energy power generation. In this context, VSG (Virtual Synchronous Generator) technology came into being and became a hot topic of research and attention in the industry. The use of virtual synchronous machine technology by new energy generator sets can enable them to autonomously participate in the operation and management of the power grid according to the operating mechanism of the synchronous machine, and respond accordingly to abnormal conditions of grid voltage / frequency, active / reactive power, so as to cope with the transient and dynamic stability problems of the power grid and resist the interference caused by external disturbances. Some of its beneficial effects have been preliminarily confirmed in research.

[0004] However, the current focus of VSG technology is mainly on how to simulate the external characteristics of synchronous generators and the stability of virtual synchronous machines connected to the grid. The impact of common working conditions such as grid voltage imbalance and grid voltage containing background harmonics is rarely mentioned, and the response strategy is relatively lacking. When a new energy unit using the VSG operation mode encounters a grid voltage drop fault, although switching it back to the CSC operation mode can deal with the unit overcurrent, it will also cause the unit to lose its VSG operating characteristics, and there is also a risk of operational instability or overcurrent when switching between the two operation modes.

[0005] When the grid voltage is unbalanced, the output power of the VSG will pulsate at twice the grid fundamental frequency (hereinafter referred to as 2 times the fundamental frequency), and the pulsation amplitude will increase with the increase of the grid imbalance and the unit power generation. The pulsation of 2 times the fundamental frequency will be reflected in the modulation wave amplitude of the VSG through the power regulation loop, causing the modulation wave to be distorted, and ultimately leading to the distortion of the output voltage and current of the VSG. In order to suppress the influence of the pulsation in the feedback power on the output voltage, the existing VSG control scheme must make the bandwidth of the active loop and the reactive loop sufficiently low [Reference "Wu Heng, Ruan Xinbo, Zhong Qingchang, et al. Modeling and parameter design of virtual synchronous generator power loop [J]. Proceedings of the CSEE, 2015, 35(24): 6508-6518."]. In this way, the flexibility of the VSG frequency modulation link design and the dynamic response capability of the frequency modulation will be limited. In addition to the problem of output voltage and current distortion, when the output current is not closed-loop controlled, the grid voltage imbalance will also introduce negative sequence current, which will bring overcurrent risks and challenges to the VSG. A resonant controller with a center frequency of 2 times the fundamental frequency is connected in parallel to the regulators of the active frequency modulation and reactive voltage regulation control loops [Reference "Sara Yazdani, Mehdi Ferdowsi, Masoud Davari, et al. "Advanced Current-Limiting and Power-Sharing Control in a PV-Based Grid-Forming Inverter Under Unbalanced Grid Conditions," IEEE Transactions on Power Electronics, vol. 8, no. 2, pp. 1084–1096, June. 2020."], which helps to suppress negative sequence current and reduce the overcurrent risk of VSG. However, the resonant regulator outputs of the active frequency modulation loop and reactive power controller of this method are superimposed on the frequency command and output voltage command of VSG respectively. The mismatch of the output amplitude and phase of the resonant regulators of the two power control loops will inevitably lead to the contradiction between negative sequence current suppression and current distortion. Summary of the invention

[0006] The present application aims to balance the three-phase output current of the virtual synchronous machine when the grid voltage is unbalanced, reduce its overcurrent risk when the grid voltage drops, and improve its operating ability to adapt to unbalanced grid voltage.

[0007] In one aspect, the present application provides an output current control method for a virtual synchronous machine to cope with grid voltage imbalance, the method comprising:

[0008] Extract the negative sequence voltage component in the voltage at the grid connection point of the virtual synchronous machine, perform phase compensation on the negative sequence voltage component, and obtain the negative sequence voltage action amount 1;

[0009] The negative sequence voltage action 1 is superimposed on the basic voltage action in the target coordinate system to obtain a final voltage action;

[0010] The final voltage action amount is modulated to generate a driving signal required for controlling the virtual synchronous machine.

[0011] In another aspect, the present application provides an output current control device for a virtual synchronous machine to cope with grid voltage imbalance, comprising:

[0012] An extraction module is used to extract the negative sequence voltage component in the voltage at the virtual synchronous machine grid connection point, and perform phase compensation on the negative sequence voltage component to obtain a negative sequence voltage action amount 1;

[0013] A synthesis module, used for superimposing the negative sequence voltage action 1 with the basic voltage action in the target coordinate system to obtain a final voltage action;

[0014] The modulation module is used to modulate the final voltage action amount to generate a driving signal required for controlling the virtual synchronous machine.

[0015] The output current control method and device of the virtual synchronous machine in response to the unbalanced grid voltage provided in the embodiment of the present application can maintain the output current balance when the grid voltage is unbalanced by extracting the negative sequence component of the grid connection point voltage of the virtual synchronous machine and performing phase compensation and then superimposing it on the basic voltage action without increasing the system cost, thereby reducing the overcurrent risk when the grid voltage drops and improving the operation ability of the virtual synchronous machine to adapt to the unbalanced grid voltage.

[0016] Specifically, on the one hand, when the grid voltage is unbalanced, the negative sequence current output by the virtual synchronous machine can be suppressed in time, thereby limiting the output current of the unit and reducing the risk of overcurrent; on the other hand, the implementation of the strategy does not involve changes to the active power control and reactive power control loops, and has little impact on the dynamic response capability of the active and reactive power control links of the virtual synchronous machine;

[0017] Compared with the existing VSG control method, while achieving the balance of the unit output current, it will not cause its output current distortion; the existing control method is generally proposed for a virtual synchronous machine with a voltage and current dual inner loop control structure, while the embodiment of the present application is the control requirement for the output current balance of a virtual synchronous machine without inner loop control under an unbalanced grid voltage. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1A block diagram of the output current control principle of the virtual synchronous machine provided in the embodiment of the present application to cope with the voltage imbalance of the power grid;

[0019] Figure 2 A schematic diagram of active power and reactive power control of a virtual synchronous machine provided in an embodiment of the present application;

[0020] Figure 3 A schematic diagram of extraction of negative sequence component of voltage at the grid connection point of a virtual synchronous machine and phase compensation provided in an embodiment of the present application;

[0021] Figure 4 A schematic diagram of generating the final voltage action amount provided in an embodiment of the present application;

[0022] Figure 5 A schematic diagram of a second-order generalized integrator provided in an embodiment of the present application;

[0023] Figure 6 A block diagram of the output current control principle of a virtual synchronous machine in response to grid voltage imbalance provided by another embodiment of the present application;

[0024] Figure 7 A virtual schematic diagram of negative sequence impedance provided by another embodiment of the present application;

[0025] Figure 8 A schematic diagram of generating a final voltage action amount provided by another embodiment of the present application;

[0026] Fig. 9 A schematic diagram of an output current control method for a virtual synchronous machine in response to grid voltage imbalance provided by an embodiment of the present application;

[0027] Fig.10 A simulation schematic diagram when the negative-sequence voltage action 1 and / or the negative-sequence voltage action 2 provided in the embodiment of the present application are not superimposed on the basic voltage action;

[0028] Fig.11 A simulation diagram of the case where the negative sequence voltage action 1 provided in the embodiment of the present application is superimposed on the basic voltage action;

[0029] Fig.12 This is a simulation diagram of the negative-sequence voltage action 1 and the negative-sequence voltage action 2 provided in an embodiment of the present application being superimposed on the basic voltage action.

[0030] The realization of the purpose, functional features and advantages of this application will be further explained in conjunction with embodiments and with reference to the accompanying drawings. DETAILED DESCRIPTION

[0031] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present application clearer and more understandable, the present application is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0032] In the description of the present application, it should be understood that the orientations or positional relationships indicated by the terms "center", "upper", "lower", "front", "back", "left", "right", etc. are based on the orientations or positional relationships shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present application. In addition, the terms "first" and "second" are used for descriptive purposes only and cannot be understood as indicating or implying relative importance.

[0033] Variables and their definitions involved in the embodiments of this application:

[0034] u oabc : Virtual synchronous machine grid connection point voltage

[0035] i oabc : Virtual synchronous machine grid-connected current

[0036] i Labc : Bridge arm output current

[0037] Z l : Grid side impedance

[0038] Z v_neg : Virtual negative sequence impedance

[0039] K neg : The gain of virtual impedance relative to the negative sequence voltage of the port

[0040] Z v_negmin : Minimum setting value of virtual impedance

[0041] P vsc , Q vsc : The active power and reactive power output by the virtual synchronous machine;

[0042] θ vsc : Phase of active power controller output

[0043] E ref : Basic voltage action amplitude output by reactive power controller

[0044] ω g : Grid voltage angular frequency

[0045] ω0: rated angular frequency of grid voltage

[0046] uox 、u oy : The x-axis and y-axis components of the voltage at the virtual synchronous machine grid connection point

[0047] u neg_x 、u neg_y : The x-axis and y-axis components of the negative sequence voltage at the virtual synchronous machine grid connection point

[0048] I neg_om : Virtual synchronous machine output current negative sequence component modulus

[0049] θ comp : Negative sequence voltage phase compensation angle

[0050] θ comp0 : Negative sequence voltage initial phase compensation angle

[0051] G ph :Phase compensation angle regulator

[0052] θ comp_dyn : Phase compensation angle regulator output

[0053] u neg_x_1 、u neg_y_1 : x- and y-axis components of negative sequence voltage action 1

[0054] U neg_om : The modulus of the negative sequence component of the voltage at the point of connection of the virtual synchronous machine

[0055] U om : Voltage modulus of virtual synchronous machine grid connection point

[0056] i ox 、i oy : The x-axis and y-axis components of the virtual synchronous machine output current

[0057] i neg_x 、i neg_y : The x- and y-axis components of the negative sequence output current of the virtual synchronous machine

[0058] u neg_x_2 、u neg_y_2 : x-axis and y-axis components of negative sequence virtual impedance voltage

[0059] e vscref_x 、e vscref_y : The x- and y-axis components of the final voltage action

[0060] e vscref_α 、e vscref_β : The α and β axis components of the final voltage action

[0061] Figure 1-Figure 5 A schematic diagram of output current control of a virtual synchronous machine in response to grid voltage imbalance provided by an embodiment of the present application.

[0062] Figure 2 A schematic diagram of the principle of a power control module provided in one embodiment of the present application.

[0063] like Figure 2 As shown, the input of the power control module is the active power P calculated based on the grid connection point voltage of the virtual synchronous machine and the output current of the virtual synchronous machine. vsc and reactive power Q vsc ; The output of the power control module is the phase θ of the virtual synchronous machine vsc , basic voltage action amplitude E ref Phase θ vsc And the basic voltage action amplitude E ref They can be calculated by the following formulas:

[0064]

[0065] E ref =G QR (Q ref -Q vsc )+U om (2)

[0066] Where, J is the inertia coefficient of the active power regulator, D is the damping coefficient; G QR is the reactive power regulator, U om It is the voltage modulus value of the virtual synchronous machine grid connection point.

[0067] Figure 3 A schematic diagram of the principle of an extraction module provided in one embodiment of the present application.

[0068] The extraction module is used to offset the influence of the negative sequence voltage of the power grid to suppress the negative sequence current output by the unit. Its input is the grid connection point voltage u oabc The αβ axis component u oα 、u oβ , the output is the x- and y-axis components u of the negative sequence voltage action 1 neg_x_1 、u neg_y_1 .

[0069] Specifically, the port voltage coordinate transformation module is first used to transform the virtual synchronous machine grid connection point voltage to the target coordinate system xy coordinate system to obtain its x and y axis components u ox 、u oy ;

[0070] When the target coordinate system is a dq coordinate system, the transformation formula of the port voltage coordinate transformation module is:

[0071]

[0072] When the target coordinate system is the αβ coordinate system, the transformation formula of the negative current coordinate transformation module is:

[0073]

[0074] Secondly, the negative sequence component extraction module is used to extract u ox 、u oy The negative sequence voltage component in the equation is u neg_x and u neg_y ;

[0075] When the aforementioned target coordinate system is a dq coordinate system, the negative sequence component extraction module can be implemented by a bandpass filter with a center frequency of 2 times the grid base frequency, and the transfer function of its output to input characteristic is:

[0076]

[0077] In the formula, ω cb is the bandwidth of the bandpass filter, ω g is the angular frequency corresponding to the fundamental frequency of the power grid.

[0078] When the target coordinate system is the αβ coordinate system, the negative sequence component extraction module can be used Figure 5 The negative sequence component extraction module based on the second-order generalized integrator is shown.

[0079] Finally, in the phase compensation module, u neg_x and u neg_y Perform phase compensation to obtain the x- and y-axis components u of the negative sequence voltage action 1 neg_x_1 、u neg_y_1 The formula for phase compensation is:

[0080]

[0081] In the formula, θ comp is the negative sequence voltage phase compensation angle, which is determined by the initial negative sequence voltage phase compensation angle θ comp0 and dynamic compensation angle θ comp_dyn The dynamic compensation angle θ comp_dyn It can be obtained by adjusting the modulus of the negative sequence component of the current output by the virtual synchronous machine. The calculation formula is:

[0082] θ comp_dyn =G ph I neg_om (6)

[0083] In the formula, I neg_om is the modulus of the negative sequence current component of the output current of the virtual synchronous machine, G ph It is a phase compensation angle regulator, and in this embodiment, it can be set as a proportional regulator.

[0084] Figure 4 A schematic diagram of the principle of a voltage action quantity synthesis module provided in one embodiment of the present application.

[0085] like Figure 4 As shown, the voltage action synthesis module converts the x-axis and y-axis components u of the negative sequence voltage action 1 into neg_x_1 、u neg_y_1 , superimposed on the basic voltage action, the α and β axis components e of the final voltage action are obtained vscref_α 、e vscref_β .

[0086] Specifically, firstly, according to the phase θ output by the virtual synchronous machine active and reactive power control module vsc and the amplitude of the basic voltage action E ref , through the basic voltage action coordinate transformation module, it is converted to the xy coordinate system to obtain the x and y axis components e of the basic voltage action ref_x_0 、e ref_y_0 .

[0087] Corresponding to the extraction module, when the target coordinate system is the dq coordinate system, the transformation formula of the basic voltage action coordinate transformation module is:

[0088]

[0089] When the target coordinate system is the αβ coordinate system, the transformation formula of the basic voltage action coordinate transformation module is:

[0090]

[0091] Secondly, the x- and y-axis components u of the negative sequence voltage action 1 are neg_x_1 、u neg_y_1 The x-axis and y-axis components e are respectively superimposed on the basic voltage action ref_x_0 、e ref_y_0 The x-axis and y-axis components e of the final voltage action are obtained. vscref_x 、e vscref_y , the integration formula is:

[0092]

[0093] Finally, the x-axis and y-axis components of the final voltage action e are transformed by the final voltage action coordinate transformation module. vscref_x 、e vscref_y Converted to the αβ coordinate system, the α and β axis components e of the final voltage action are obtained vscref_α 、e vscref_β .

[0094] When the target coordinate system is a dq coordinate system, the transformation formula of the final voltage action coordinate transformation module is:

[0095]

[0096] When the target coordinate system is the αβ coordinate system, the transformation formula of the final voltage action coordinate transformation module is:

[0097]

[0098] The modulation module converts the α and β axis components of the final voltage action into vscref_α 、e vscref_β Through PWM modulation, for example, a three-phase space vector modulation method is adopted to generate a PWM driving signal required for virtual synchronous machine control.

[0099] Fig.10 When the negative sequence voltage action 1 and / or the negative sequence voltage action 2 are not superimposed on the basic voltage action, the single-phase grid voltage drops by 20% and lasts for 0.5s during the operation of the virtual synchronous machine, and then returns to normal simulation results.

[0100] Fig.11 is the simulation result after the negative sequence voltage action 1 is superimposed on the basic voltage action. Fig.10 In contrast, when the grid voltage is unbalanced, the negative sequence current output by the virtual synchronous machine can be suppressed in time, thereby limiting the output current of the unit and reducing the risk of overcurrent. While achieving the balance of the unit output current, it will not cause its output current distortion.

[0101] Figure 6-Figure 8 A schematic diagram of output current control of a virtual synchronous machine in response to grid voltage imbalance provided by another embodiment of the present application.

[0102] and Figure 1-Figure 5 The difference of the example is that it also includes a negative sequence impedance virtual module, which is used to virtually generate a negative sequence impedance at the output end of the virtual synchronous machine to suppress the negative sequence current.

[0103] like Figure 7 As shown, the output current of the virtual synchronous machine is first transformed into the target coordinate system xy using the current coordinate transformation module to obtain its x and y axis components i ox 、i oy ; When the target coordinate system is the dq coordinate system, the transformation formula of the current coordinate transformation module is:

[0104]

[0105] When the target coordinate system is the αβ coordinate system, the transformation formula of the current coordinate transformation module is:

[0106]

[0107] Secondly, the negative sequence component extraction module is used to extract i ox and i oy The negative sequence current component in the equation is i neg_x and i neg_y ;

[0108] When the aforementioned target coordinate system is a dq coordinate system, the negative sequence component extraction module can be implemented by a bandpass filter with a center frequency of 2 times the grid base frequency, and the transfer function of its output to input characteristic is:

[0109]

[0110] In the formula, ω cb is the bandwidth of the bandpass filter, ω g is the angular frequency corresponding to the fundamental frequency of the power grid.

[0111] When the target coordinate system is the αβ coordinate system, the negative sequence component extraction module can be used Figure 5 The negative sequence component extraction module based on the second-order generalized integrator is shown.

[0112] Finally, the extracted negative sequence current component i neg_x and i neg_y With specific virtual impedance Z v_neg Multiply them to get the x- and y-axis components u of the negative sequence voltage action 2 neg_x_2 、u neg_y_2 .

[0113] Virtual impedance Z v_neg It increases with the increase of the modulus of the negative sequence component of the grid voltage.

[0114] In this example, Z v_neg Set it as follows:

[0115] Z v_neg =Z v_negmin +K neg U neg_om (12)

[0116] In the formula, Z v_negmin >0 is the minimum setting value of virtual impedance, K neg >0 is the gain of virtual impedance, U neg_om is the modulus of the negative sequence voltage component of the virtual synchronous machine grid connection point voltage.

[0117] like Figure 8 As shown, the voltage action synthesis module converts the x-axis and y-axis components u of the negative sequence voltage action 2 into neg_x_2 u neg_y_2and the x- and y-axis components u of the negative sequence voltage action 1 neg_x_1 、u neg_y_1 , superimposed on the basic voltage action output by the power control module, and the α and β axis components e of the final voltage action are obtained. vscref_α 、e vscref_β .

[0118] Specifically, firstly, according to the phase θ output by the virtual synchronous machine active power and reactive power control module vsc and the amplitude of the basic voltage action E ref , through the basic voltage action coordinate transformation module, it is converted to the xy coordinate system to obtain the x and y axis components e of the basic voltage action ref_x_0 、e ref_y_0 .

[0119] When the target coordinate system is a dq coordinate system, the transformation formula of the basic voltage action coordinate transformation module is:

[0120]

[0121] When the target coordinate system is the αβ coordinate system, the transformation formula of the basic voltage action coordinate transformation module is:

[0122]

[0123] Secondly, the x- and y-axis components u of the negative sequence voltage action 2 are neg_x_2 、u neg_y_2 and the x- and y-axis components u of the negative sequence voltage action 1 neg_x_1 、u neg_y_1 The x-axis and y-axis components e are respectively superimposed on the basic voltage action ref_x_0 、e ref_y_0 The x-axis and y-axis components e of the final voltage action are obtained. vscref_x 、e vscref_y , the integration formula is:

[0124]

[0125] Finally, the x-axis and y-axis components of the final voltage action e are transformed by the final voltage action coordinate transformation module. vscref_x 、e vscref_y Converted to the αβ coordinate system, the α and β axis components e of the final voltage action are obtained vscref_α 、e vscref_β .

[0126] When the target coordinate system is a dq coordinate system, the transformation formula of the final voltage action coordinate transformation module is:

[0127]

[0128] When the target coordinate system is the αβ coordinate system, the transformation formula of the final voltage action coordinate transformation module is:

[0129]

[0130] The modulation module converts the α and β axis components of the final voltage action into vscref_α 、e vscref_β Through PWM modulation, for example, a three-phase space vector modulation method is adopted to generate a PWM driving signal required for virtual synchronous machine control.

[0131] Fig.10 When the negative sequence voltage action 1 and / or the negative sequence voltage action 2 are not superimposed on the basic voltage action, the single-phase grid voltage drops by 20% and lasts for 0.5s during the operation of the virtual synchronous machine, and then returns to normal simulation results.

[0132] Fig.12 is the simulation result after the negative sequence voltage action 1 and the negative sequence voltage action 2 are superimposed on the basic voltage action. Fig.10 In contrast, when the grid voltage is unbalanced, the negative sequence current output by the virtual synchronous machine can be suppressed in time, thereby limiting the output current of the unit and reducing the risk of overcurrent. While achieving the balance of the unit output current, it will not cause its output current distortion.

[0133] Fig. 9 Schematic diagram of an output current control method for a virtual synchronous machine to cope with grid voltage imbalance provided in an embodiment of the present application.

[0134] like Fig. 9 As shown, the method includes:

[0135] Step S11, extracting the negative sequence voltage component in the voltage at the grid connection point of the virtual synchronous machine, and performing phase compensation on the negative sequence voltage component to obtain a negative sequence voltage action amount 1;

[0136] Step S12, superimposing the negative sequence voltage action 1 with the basic voltage action in the target coordinate system to obtain a final voltage action;

[0137] Step S13: modulate the final voltage action to generate a driving signal required for controlling the virtual synchronous machine.

[0138] In one example, extracting the negative sequence voltage component in the grid connection point voltage of the virtual synchronous machine includes:

[0139] Performing coordinate transformation on the grid-connected point voltage of the virtual synchronous machine to obtain voltage components in a target coordinate system;

[0140] The voltage component in the target coordinate system is extracted to obtain the negative sequence voltage component.

[0141] In one example, phase compensation is performed on the negative sequence voltage component by using an initial phase compensation angle and / or a dynamic compensation angle.

[0142] In one example, coordinate transformation is performed on the phase and amplitude of the basic voltage action of the virtual synchronous machine to obtain the basic voltage action in the target coordinate system.

[0143] In one example, the method further includes:

[0144] According to the voltage of the virtual synchronous machine grid connection point and the output current of the virtual synchronous machine, the active power and reactive power of the virtual synchronous machine are calculated;

[0145] According to the active power and reactive power of the virtual synchronous machine, the phase and basic voltage action amplitude of the virtual synchronous machine are calculated.

[0146] In one example, the negative sequence voltage action 1 is superimposed on the basic voltage action in the target coordinate system to obtain the final voltage action, and the process also includes:

[0147] Extracting a negative sequence current component from the output current of the virtual synchronous machine; multiplying the negative sequence current component by a specific virtual impedance to obtain a negative sequence voltage action 2;

[0148] The negative sequence voltage action 1 is superimposed on the basic voltage action in the target coordinate system to obtain the final voltage action, including:

[0149] The negative sequence voltage action 1, the negative sequence voltage action 2 and the basic voltage action in the target coordinate system are superimposed to obtain a final voltage action.

[0150] In one example, the virtual impedance includes at least one of resistive impedance, inductive impedance, and resistive-inductive impedance.

[0151] In one example, the virtual impedance is proportional to the modulus of the negative sequence voltage component of the grid connection point voltage of the virtual synchronous machine.

[0152] In one example, the output current of the virtual synchronous machine includes a grid-connected point current or a bridge arm current.

[0153] In one example, extracting the negative sequence current component in the output current of the virtual synchronous machine includes:

[0154] Performing coordinate transformation on the output current of the virtual synchronous machine to obtain a current component in a target coordinate system;

[0155] The current component in the target coordinate system is extracted to obtain the negative sequence current component.

[0156] In one example, the target coordinate system includes a dq coordinate system or an αβ coordinate system.

[0157] The preferred embodiments of the present application are described above with reference to the accompanying drawings, but the scope of the present application is not limited thereby. Any modification, equivalent substitution and improvement made by a person skilled in the art without departing from the scope and essence of the present application shall be within the scope of the present application.

Claims

1. A method for controlling output current of a virtual synchronous machine in response to voltage imbalance in a power grid, characterized in that: The method comprises: Extract the negative sequence voltage component (u neg_x 、u neg_y ) and the negative sequence voltage component (u neg_x 、u neg_y ) performs phase compensation and obtains the negative sequence voltage action amount 1; The negative sequence voltage action 1 is compared with the basic voltage action (e ref_x_0 、e ref_y_0 ) are superimposed to obtain the final voltage action (e vscref_α 、e vscref_β ); The final voltage action (e vscref_α 、e vscref_β ) is modulated to generate a driving signal required for virtual synchronous machine control; The negative sequence voltage action 1 is compared with the basic voltage action (e ref_x_0 、e ref_y_0 ) to be superimposed, and previously also included: Extracting a negative sequence current component from the output current of the virtual synchronous machine; multiplying the negative sequence current component by a specific virtual impedance to obtain a negative sequence voltage action 2; the virtual impedance includes at least one of a resistive impedance, an inductive impedance, and a resistive-inductive impedance; The negative sequence voltage action 1 is compared with the basic voltage action (e ref_x_0 、e ref_y_0 ) are superimposed to obtain the final voltage action (e vscref_α 、e vscref_β ),include: The negative sequence voltage action 1, the negative sequence voltage action 2 and the basic voltage action (e ref_x_0 、e ref_y_0 ) are superimposed to obtain the final voltage action (e vscref_α 、e vscref_β ).

2. The method according to claim 1, characterized in that The negative sequence voltage component (u neg_x 、u neg_y ),include: The coordinate transformation of the grid-connected point voltage of the virtual synchronous machine is performed to obtain the voltage component (u ox 、u oy ); The voltage component (u ox 、u oy ) is extracted to obtain the negative sequence voltage component (u neg_x 、u neg_y ).

3. The method according to claim 1, characterized in that The negative sequence voltage component (u neg_x 、u neg_y ) for phase compensation.

4. The method according to claim 1, characterized in that: The phase (θ vsc ) and the basic voltage action amplitude (E ref ) to transform the coordinates and obtain the basic voltage action (e ref_x_0 、e ref_y_0 ).

5. The method according to claim 4, characterized in that The method further comprises: According to the voltage of the virtual synchronous machine grid connection point and the output current of the virtual synchronous machine, the active power and reactive power of the virtual synchronous machine are calculated; According to the active power and reactive power of the virtual synchronous machine, the phase (θ vsc ) and the basic voltage action amplitude (E ref ).

6. The method according to claim 1, characterized in that The virtual impedance and the negative sequence voltage component (u neg_x 、u neg_y ) is proportional to the modulus value.

7. The method according to claim 1, characterized in that The output current of the virtual synchronous machine includes a grid-connected point current or a bridge arm current.

8. The method according to claim 1, characterized in that The step of extracting the negative sequence current component in the output current of the virtual synchronous machine comprises: Performing coordinate transformation on the output current of the virtual synchronous machine to obtain a current component in a target coordinate system; The current component in the target coordinate system is extracted to obtain the negative sequence current component.

9. An output current control device for a virtual synchronous machine to cope with voltage imbalance in a power grid, characterized in that: include: Extraction module, used to extract the negative sequence voltage component (u neg_x 、u neg_y ) and the negative sequence voltage component (u neg_x 、u neg_y ) performs phase compensation and obtains the negative sequence voltage action amount 1; The extraction module is also used to extract the negative sequence current component in the output current of the virtual synchronous machine; multiply the negative sequence current component by a specific virtual impedance to obtain a negative sequence voltage action 2; the virtual impedance includes at least one of a resistive impedance, an inductive impedance and a resistive-inductive impedance; A synthesis module is used to combine the negative sequence voltage action 1 with the basic voltage action (e ref_x_0 、e ref_y_0 ) are superimposed to obtain the final voltage action (e vscref_α 、e vscref_β ); The synthesis module is also used to combine the negative sequence voltage action 1, the negative sequence voltage action 2 and the basic voltage action (e ref_x_0 、e ref_y_0 ) are superimposed to obtain the final voltage action (e vscref_α 、e vscref_β ); A modulation module is used to modulate the final voltage action amount (e vscref_α 、e vscref_β ) is modulated to generate the driving signal required for virtual synchronous machine control.

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